Furnace plants for heat treatment of workpieces under protective gas atmospheres

ABSTRACT

Furnace plants for the heat treatment of metal workpieces under protective atmospheres are provided with one prechamber servicing two or more heat treating chambers.

United States Patent [72] Inventors Karl-Heinz Winter Domigheim; Friedrich Eysell, Frankfurt am Main; Rolf Schuster. Hanau (Main), all of, Germany [2| Appl, No. 830,729

[22] Filed June 5,1969

[45] Patented June l, [971 [73] Assignee Deutsche Gold-und Silber Sheideanstalt normals Rossler Frankfurt, am Main, Germany [32] Priority June 5, 1968 [3 3 Germany [54] FURNACE PLANTS FOR HEAT TREATMENT OF WORKPIECES UNDER PROTECTIVE GAS [5]] lnt.Cl C2ld 1/00, F27b 9/02 [50] Field of Search 263/36, 37, 3s, 39; 266/4 [56] References Cited UNITED STATES PATENTS 2,000,664 5/1935 Hayes 263/36 2,978,237 4/! 961 Frank 263/6 3,] 37,485 6/1964 Johnson et a]. 263/6 3,431,346 3/1969 Westeren et al. 263/36X Primary Examiner-John .l. Camby Attorney-Cushman, Darby & Cushman ABSTRACT: Furnace plants for the heat treatment of metal workpieces under protective atmospheres are provided with one prechamber servicing two or more heat treating chambers.

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SHEET 2 0F 2 FiQZ ATTORNEY 5 FURNACE PLANTS FOR HEAT TREATMENT OF WORKI'IECES UNDER PROTECTIVE GAS ATMOSPHERES There are known furnaces in which metal workpieces are carburizcd, carbonitrided, gas nitrided, normalized, brazed, sintered, steam treated and hardened or tempered. These furnaces are designed as continuous furnaces or as furnaces for intermittent operation, for example as chamber or pit furnaces.

In a continuous furnace, the single process steps take place in a closed unit logically one after the other. As examples there can be mentioned: preheating, carburizing, lowering of the temperature to hardening temperature, quenching and tempering.

The intermittently operating furnaces are known as single furnaces and consist in general of a prechamber and the true carburizing or hardening furnace. The prechamber serves once as loading assist means in order that the protective gas atmosphere in the carburizing or hardening furnace is not influenced in the charging operation. In addition, the prechamber is provided with the quenching tank and a cooling station for cooling the workpieces under protective gas. A lifting device in the prechamber serves to lower and lift the treated goods. A mechanical conveyor arrangement passes the loaded charging support into the furnace and onto the loading or unloading table before the furnace. The mentioned conveyor is a constituent of the prechamber.

By another of the known furnace designs, the prechamber is found behind the carburizing or hardening furnace. With this furnace design, however, the protective gas atmosphere in the carburizing or hardening furnace is partially disturbed during the period of charging.

Also furnace designs are known according to which two heat-treating chambers are arranged one behind the other, in order, for example, to be able to work in the first chamber at carburizing temperature and in the second chamber at the lower hardening temperature.

In the last described furnace designs for intermittent operation there is the drawback that on account of the necessary, thin walled internal doors no definite temperature and protective gas conditions (dewpoint or CO, value) can be accurately maintained. Besides with all of these furnace types it is only possible to work at the same time cycle in both chambers, i.e. the programmed heat treatment conditions (treating time, temperature and type of protective gas) cannot be different for the two chambers. Furthermore the cooling medium (protective gas, oil, salt, water) cannot be varied.

According to the invention it is proposed with use of a single conveyor, for example following German Pat. No. 1,279,706 (application P 14 58987.8), to fit several heat-treating chambers on only one prechamber and thereby to eliminate the portrayed drawbacks and limitations of the known'types of furnace. Without difficulty, for example, the following heat treatment processes can be accomplished according to the invention.

1. All of the heat-treating chambers fitted to the gastight prechamber are used as carburizing furnaces.

2. One or two heat-treating chambers work as carburizing furnaces, while in a further heat-treating chamber the workpiece is brought to hardening temperature prior to cooling, for example in oil.

-3. The first heat-treating chamber is used for carburizing, in the second heat-treating chamber the workpieces are transformed into the pearlitic structure and in the third heat-treating chamber the workpieces are reheated to hardening temperature prior to quenching.

The invention will be understood best in connection with the drawings wherein:

FIG. 1 is a diagrammatic front view of a furnace plant according to the invention; and

FIG. 2 is a diagrammatic plan view of the furnace plant of FIG. 1.

Referring now specifically to the drawings, the furnace plant of the invention consists of two or more heat-treatin chambers l, a gastight prechamber 2 and a loading or unloa ing table 3. In the prechamber there is shown by the numeral 4 the position of a loaded charging table before being carried on into a heat-treating chamber or before being discharged onto the unloading table 3. The numeral 5 shows the charging table in the cooling medium and the numeral 6 the position of the charging table during the cooling period under protective gas atmosphere which becomes strongly circulated by a gas circulation device 7 to increase the convection. The rotary-lifting device 8 also carries the mechanical conveyor 9 firmly mounted on it. The door 10 seals the prechamber tight against the outside atmosphere. In order to be able to cool altematively in oil, salt or water the bottom part of the prechamber, which contains the cooling medium, is able to be moved out. The protective gas in the proper formulation depending on the intended use is passed separately and under controlled pressure to the prechamber and the heat-treating chambers.

The heat-treating chambers can be provided on their backwalls with doors 11 through which the heat-treated workpieces can be immersed in additional cooling baths or withdrawn for press hardening, further machining, etc.

The furnace plant can be provided with automatic switch potentiometers and gas meter instruments so that the entire heat treatment cycle takes place automatically.

We claim:

1. A furnace plant for the heat treatment of workpieces under a protective gas atmosphere comprising: means defining a single gastight unheated prechamber having a horizontally facing loading and unloading door for workpieces; means defining at least two heat-treating chambers disposed in a common horizontal plane and adjacent said prechamber; a separate door between said prechamber and each of said heattreating chambers; conveying means wholly within said prechamber, said conveying means being adapted to be turned to align workpieces with any of said separate doors so that the workpieces can subsequently be moved between said prechamber and any of said heat-treating chambers.

2. A furnace plant according to claim ll having a quenching bath in the bottom portion of the prechamber in movable arrangement so as to assure an easy change of a cooling medi- 3. A furnace plant according to claim 1 wherein the heattreating chambers are provided on their backwalls with doors through which the heat-treated workpieces can be passed for further treatment.

4. A furnace plant according to claim I wherein the prechamber includes means for lifting and lowering the goods being treated in said chamber.

5. A furnace plant according to claim 1 wherein at least two of the heat-treating chambers connected to a single prechamber are maintained at different temperatures. 

1. A furnace plant for the heat treatment of workpieces under a protective gas atmosphere comprising: means defining a single gastight unheated prechamber having a horizontally facing loading and unloading door for workpieces; means defining at least two heat-treating chambers disposed in a common horizontal plane and adjacent said prechamber; a separate door between said prechamber and each of said heat-treating chambers; conveying means wholly within said prechamber, said conveying means being adapted to be turned to align workpieces with any of said separate doors so that the workpieces can subsequently be moved between said prechamber and any of said heat-treating chambers.
 2. A furnace plant according to claim 1 having a quenching bath in the bottom portion of the prechamber in movable arrangement so as to assure an easy change of a cooling medium.
 3. A furnace plant according to claim 1 wherein the heat-treating chambers are provided on their backwalls with doors through which the heat-treated workpieces can be passed for further treatment.
 4. A furnace plant according to claim 1 wherein the prechamber includes means for lifting and lowering the goods being treated in said chamber.
 5. A furnace plant according to claim 1 wherein at least two of the heat-treating chambers connected to a single prechamber are maintained at different temperatures. 